Vehicles having an internal combustion engine can operate in a variety of modes. As one example, an engine may operate in a spark ignition (SI) mode, wherein a charge of a mixture of air and fuel is ignited by a spark performed by a sparking device within a combustion chamber. As another example, an engine may operate in a compression ignition mode, wherein a mixture of air and fuel are compressed within a combustion chamber by a piston, causing ignition of the charge without necessarily requiring the addition of a spark from a sparking device.
One type of compression ignition known as homogeneous charge compression ignition (HCCI) utilizes compression of a substantially homogeneous mixture of air and fuel to achieve controlled auto-ignition (CAI). In HCCI engines, ignition occurs virtually simultaneously throughout a combustion chamber as a result of compression instead of spark ignition, making the combustion process challenging to control.
In one approach, described in SAE 2005-01-0762, a mixed SI and HCCI combustion mode is described in an 8-stroke cycle. Specifically, SI combustion may be used to increase charge exhaust temperature to assist in HCCI combustion on the next cycle. However, such operation may result in decreased efficiency due to the SI combustion event utilized with the HCCI combustion. The inventors herein have recognized the above-mentioned disadvantages and have developed a system that uses electronic valve actuation (EVA) and HCCI combustion in a multi-stroke mode by cycling a cylinder charge back into an intake to improve mixing of fuel and air charge for initiating or maintaining HCCI combustion.
One example approach to overcome at least some of the disadvantages of prior approaches includes operating a multi-stroke homogeneous charge compression ignition engine having a plurality of cylinders using electronic valve actuation, comprising: actuating at least one intake valve of a cylinder with a late intake valve opening (LIVO); receiving an air and fuel charge in the cylinder; opening the at least one intake valve during a compression stroke of a piston in the cylinder to cycle the air and fuel charge into an intake manifold to mix the air and fuel charge; opening the at least one intake valve to receive at least some of the mixed air and fuel charge from the intake manifold during an intake stroke; and compressing the mixed air and fuel charge to auto-ignition to generate HCCI combustion without applying spark ignition to the mixed air and fuel charge.
Operation according to various of the embodiments described herein may provide various advantages. In particular, by mixing an air and fuel charge and cycling it back into an intake passage, improved control of HCCI combustion and timing may be achieved in subsequent combustion, such as the next one to several, or more, combustions. Also, while such operation may assist in transitioning combustion modes, it may also be used to perpetuate HCCI combustion.
The above potential advantages and other advantages, and features will be readily apparent from the following Detailed Description and/or accompanying drawings.